1) Field of the Invention
The present invention relates to a modified polyamine, an aqueous epoxy resin curing agent using the same and processes for producing thereof. Aqueous epoxy resin curing agents are widely used in industrial fields such as coatings being used for the purpose of anticorrosion or decoration, adhesives for civil and building work and the like.
2) Prior Art
Epoxy resins have been widely used in the above-mentioned industrial fields by virtue of many more excellent charateristics including adhesive property, heat resistance, chemical resistance, electrical properties, mechanical properties, etc., for various substrates than those of other types of resins. Generally, the form of epoxy resin composition being used in the field of coating and adhesive is classified broadly into a liquid type containing no solvent (solventless type), a liquid type containing an organic solvent as main medium (organic solvent type), a liquid type containing water as medium (aqueous composition) and solid (powder) type (powder composition).
Among the above-mentioned types, the solventless type is a composition wherein its viscosity has been lowered by adding a low-viscosity curing agent and a high boiling point diluent to an epoxy resin in the form of liquid at ordinary temperature. However, it is inevitable that, in the course of producing a low-viscosity curing agent, a large amount of free amines and phenols harmful to the human body has to be used, and even in case of a diluent doing comparatively small harm to human body, the use of such diluent causes deterioration in the performance of a curing agent.
In the organic solvent type, a high molecular weight epoxy resin in the form of solid at ordinary temperature is generally dissolved in a low-viscosity solvent such as xylene, toluene, cellosolve, ethanol, n-butanol, etc., and the range of curing agent which can be selected is wide. Accordingly, the organic solvent type not only affords a high-performance cured product, but also permits optional adjustment of viscosity of the composition, and thus is often used for the above-mentioned purpose. Nevertheless, regulation for use of solvent has been become stringent year by year due to problems including harmfulness to workers handling such organic solvents, such hazard as fire or explosion and environmental pollution such as air pollution.
The powder type composition, which is mainly used as a coating, is a combination of a solid epoxy resin with a solid curing agent, but use thereof is limited with regard to its workability.
The aqueous type composition is obtained by dispersing or dissolving an epoxy resin and a curing agent in water and is a composition with excellent workability free from the above-mentioned drawbacks which are inherent in other types of compositions except properties of cured product.
Conventional aqueous epoxy resin compositions had the disadvantage that an emulsifier using for formation of a stable emulsion exerted bad influence on properties of cured epoxy product. U.S. Pat. No. 4,197,389 and Japanese Patent Application Laid-Open No. 6-179801 each disclose a curing agent having a self-emulsifiable property. Since in the former a catalyst being used in synthesis is mixed in a curing agent and in the latter aliphatic diglycidyl ether having a comparatively high chlorine content is generally used, products using such curing agents had disadvantages that properties of the cured products, particularly water resistance, were inferior.